Adipose tissue or body fat is a connective tissue derived from mesenchyme made up of the association of cells which accumulate lipids in their cytoplasm: adipocytes. The adipose tissue of mammals can be classified into two types: white adipose tissue and brown adipose tissue. White adipose tissue is the predominant tissue, formed by unilocular adipocytes which accumulate their entire lipid content in just one drop, and whose main function is the accumulation of energy reserves in the form of triglycerides. Brown adipose tissue which less common and is formed by multilocular adipocytes and usually disappears soon after birth, being particularly relevant in hibernating mammals. In humans, fetuses and newborns present brown adipose tissue in their cervical, axillary, peri-renal and peri-adrenal deposits; in adults, however, there are no brown fatty deposits but instead there are populations of multilocular adipocytes intercalated between white adipose tissue. Brown adipose tissue is highly thermogenic, it has a large number of mitochondria in its cytoplasm and high levels of mitochondrial gene expression, and its function consists of energy dissipation in the form of heat.
One of the distinctive features of adipose tissue is its plasticity. This plasticity is a particular result of the ability of the adipose tissue to change its volume either because of a change in the amount of intracellular lipids (increase in size of adipocytes) or due to the change in number of the adipocytes. Mature adipocytes accumulate fat as a source of energy (i.e. excess calorie intake) and are able to release it in the case that energy is needed (i.e. periods of fasting, exposure to cold, etc.). The number of mature adipocytes is maintained more or less constant from adulthood. However, adipocyte precursor cells or pre-adipocytes are continually multiplied and differentiate into mature adipocytes able to accumulate fat. This mechanism is called differentiation or adipogenesis.
Adipogenesis is principally characterized by a morphological modification of the precursor cells, a phenotype change and the appearance of adipocyte-specific markers. When differentiation begins, the majority of genes are activated, among them PPARγ (peroxisome proliferator-activated receptor-γ). PPARγ, a member of the PPAR nuclear receptor family which is expressed in adipose tissue, is a master regulator of adipocyte differentiation [Tontonoz P. et al., “Regulation of adipocyte gene expression and differentiation by peroxisome proliferator activated receptor gamma”. Curr. Opin. Genet. Dev., (1995), 5(5), 571-576]. These receptors act as transcription factors and regulate gene expression in cell differentiation processes. PPARγ is essential in adipose tissue and forms heterodimers with the retinoid X receptors which are bound to specific regions in the DNA of the target genes and regulate their expression. The genes activated by PPARγ stimulate lipid uptake by the fatty cells and strongly induce white adipose tissue differentiation. PPARγ knockout mice are capable of producing adipose tissue when they are fed on a diet high in fat [Jones J. R. et al., “Deletion of PPARgamma in adipose tissues of mice protects against high fat diet-induced obesity and insulin resistance”. Proc. Natl. Acad. Sci. U.S.A., (2005), 102(17), 6207-6212].
PPARγ has a transcriptional role in the differentiation of pre-adipocytes into mature adipocytes, since it has been seen that PPARγ activation through ligand binding gives rise to the accumulation of lipids, morphological changes and promotes the expression of adipose tissue-specific genes [Tontonoz P. et al., “Stimulation of adipogenesis in fibroblasts by PPARγ2, a lipid-activated transcription factor”, (1994), Cell, 79, 7355-7359]. In addition, there is data which demonstrates that adipogenesis stimulation due to PPARγ activation through ligand binding also occurs in vivo [Okuno A. et al., “Troglitazone increases the number of small adipocytes without the change of white adipose tissue mass in obese Zucker rats”. J. Clin. Invest., (1998), 101, 1354-1361]. The involvement of PPARγ in adipogenesis is also supported by the fact that patients with a mutation in PPARγ which makes this receptor constantly activated present greater adipocyte differentiation and obesity [Ristow M. et al., “Obesity associated with a mutation in a genetic regulator of adipocyte differentiation”. N. Engl. J. Med., (1998), 339, 953-959]. The mechanism by which PPARγ stimulates adipogenesis seems to be related to its mediating effect of the cell cycle arrest [Classon M. et al., “Opposing roles of pRB and p107 in adipocyte differentiation”. P.N.A.S., (2000), 97, 10826-10831], since, in general cell division and cell differentiation are considered to be mutually exclusive processes.
Serious efforts have been made by the pharmaceutical to developing new PPARγ modulatory compounds with the aim of slowing down the advance of obesity and type 2 diabetes in developed countries. PPARγ agonists have also been described for the treatment and/or prevention of disorders or diseases of the skin such as disorders due to keratinocyte hyperproliferation such as psoriasis, lichen planus, skin lesions associated with lupus, dermatitis such as atopic, seborrheic or solar dermatitis, keratosis such as seborrheic, senile, actinic, photoinduced or follicular keratosis, acne vulgar, nevus, keloids or wrinkles among others [WO 95/535108 A1; EP 1041977 B1; WO 2009/153373 A2; Krentz A. J. et al., “Type 2 diabetes, psoriasis and thiazolidinediones”, (2006), Int. J. Clin. Pract., 60, 362-363], keratinization disorders such as common acne, comedones, polymorphous, rosacea, nodulocystic acne, conglobate acne, senile acne, ichthyosis, Darier's disease, keratodermia palmoplantaris, leukoplakia, mucosal lichen or cutaneous lichen; conditions with an inflammatory component such as cutaneous psoriasis, mucosal or nail psoriasis, psoriatic rheumatism, cutaneous atopia including eczema; dermal proliferations such as common warts, flat warts, epidermodysplasia verruciformis, oral papillomatosis; immune dermatoses such as lupus erythematosus, bullous diseases, scleroderma, skin aging, actinic keratosis, and pigmentation disorders [EP 1781297 B1], alopecia greata or vitiligo [EP 1331934 B1], cutaneous lipid metabolism disorders such as hyperseborrhea of acne and simple seborrhea [EP 1781297 B1], regulation of the fibroblasts or myofibroblasts function, excess of extracellular matrix production, healing or reepithelialization processes, nodular fascitis or Dupuytren's contracture [US 2004/0152746 A1; US 2008/0182780 A1] among others.
PPAR receptors are transcription factors which regulate adipocyte-specific gene expression, but there is another level of regulation formed by a group of proteins which modulate these transcription factors: transcriptional coactivators. A transcription coactivator is a protein complex which increases the transcription rate of its target by interacting with transcription factors but does not recognize nor is it bound to specific DNA sequences. These complexes comprise proteins which mediate the anchorage in the transcription and protein factors which exercise specific functions, such as the modification of histones through acetyltransferase activity, through phosphorylation and through methylation, unwinding and remodeling ATP-dependent chromatin, and others. Coactivators are recruited to the target genes by protein-protein interactions with transcription factors which are bound to DNA. The latter modify the structure of the chromatin in the target gene by association with the RNA polymerase machinery, giving rise to an increase in the transcription of the target genes. Interactions between coactivators and DNA-binding factors are specific, and depend on the presence of certain protein interfaces and signals which activate transcription factors. These interactions are highly versatile: the same coactivator can interact with multiple transcription factors, and a transcription factor can interact with several coactivators. The possibility of regulating gene expression by modulation of transcription coactivators opens the door to their study for therapeutic purposes.
In mammals, one of the most notable examples of the regulation of metabolic routes by transcription coactivators is PPARγ coactivator 1α [Handschin C. et al., “Peroxisome proliferator-activated receptor gamma coactivator 1 coactivators, energy homeostasis, and metabolism” Endocr Rev., (2006), 27(7), 728-735]. PGC-1α is activated by signals which control energy and nutrient homeostasis. PGC-1α activates gene expression through specific interaction with transcription factors, among them PPARγ, which are bound to metabolism gene promoters. The fact that PGC-1α controls the activity of PPARγ suggests that it can be a target for the development of compounds useful in the treatment and/or care of those conditions, disorders and/or diseases mediated by PPARγ, such as obesity, type 2 diabetes, resistance to insulin, or skin complaints due to keratinocyte hyperproliferation disorders, keratinization disorders or healing or reepithelialization processes, among others.
It has been described in the bibliography that during the adipogenesis process the PGC-1α expression levels increase independently of PPAR [Semple R. C. et al., “Expression of the thermogenic nuclear hormone receptor coactivator PGC-1α is reduced in the adipose tissue of morbidly obese subjects”. Int. J. Obes., (2004), 28, 176-179] which suggests that PGC-1α is a potential target per se for processes in which the regulation of adipogenesis is desirable and, therefore, the regulation of the volume of adipose tissue.
Described in the prior art are PGC-1α modulators not solely for treating obesity, type 2 diabetes or the resistance to insulin [US 2009/0029933 A1], but also for the treatment of neurological disorders and diseases [US 2009/0005314 A1] or to regulate the formation of type I muscular fibers [US 2006/0035849 A1].
The variable distribution of adipose tissue is what defines the body's figure and facial shape. Subcutaneous adipose tissue is located in places such as the cheeks, lips, eyelids, extremities, hands, buttocks, thighs and bust. An increase in the volume of the subcutaneous adipocytes in certain areas of the human body can be related to smooth skin and a youthful, healthy appearance, as with the face, whilst in other areas it is considered an undesired aesthetic defect, as it happens with the thighs. Thus, regulation of PGC-1α and therefore, regulation of the volume of adipose tissue is an objective not just for the pharmaceutical sector, due to its potential benefit in the treatment and/or prevention of different disorders or diseases such as obesity, type 2 diabetes, neurological disorders and diseases and the resistance to insulin, but also by the cosmetic sector with the aim of shaping ones figure.
With age, facial marks such as expression lines appear to be normal, due to the senescence of the cells which make up the skin, due to elastosis, to a decrease in collagen levels and lipoatrophy. The gradual loss of subcutaneous fat greatly contributes to skin sagging, greater depth of wrinkle furrows, greater skin dryness, and in general results in thinner and weaker skin. This effect is clearly visible on the hands and the lower part of the neck and neckline. Likewise, some diseases involve lipolytic processes which are clearly visible on the face, as is the case of acquired immune deficiency syndrome (AIDS), stigmatizing the sufferer. Therefore, the increase in the volume of adipose tissue in the areas affected by lipoatrophy or lipodystrophy is of interest to restore a more youthful appearance. Likewise, an increase in the layer of subcutaneous adipocytes is also desirable in the case of women who wish to increase the size of their breasts or buttocks. The breasts are formed by mammary glands, connective tissue and adipose tissue. The volume of adipose tissue is variable, and therefore it is a determining factor of the volume and shape of the breast. Topical application of compounds that decrease lipolysis and/or increase lipogenesis or adipogenesis presents many advantages over usual process for breast enlargement, such as silicone breast implants or tissue transplants, invasive techniques which require surgery and are not risk free.
The decrease in the volume of adipose tissue is also an aim of the cosmetics and aesthetics industry, since at present there are no satisfactory solutions for the treatment and/or prevention of cellulitis. Cellulitis is an adipose and subcutaneous tissue condition which is characterized by providing the skin with a characteristic and aesthetically unpleasant orange peel appearance. Also called local lipodystrophy, cellulitis mainly and almost exclusively affects women, and can be considered a trait of sexual dimorphism. The common areas for the formation of cellulitis are the thighs, buttocks, upper arms, and less frequently, the back part of the neck and the lower legs. Although local lipodystrophy or cellulitis is not synonymous with obesity or being overweight, there is a correlation between cellulitis and adipose tissue hypertrophy. The origin of cellulitis is not well defined, but it is known that, as well as the excess of adipose tissue, its appearance is due to several causes. One of them is the difference between sexes in the histological distribution of the subcutaneous fat lobes due to differences in the connective adipose tissue septa: males have diagonal septa and small lobes, whilst the septa in women are rectangular and the lobes are larger. Another cause may be the existence of changes to the microvascular network which irrigates the adipose tissue. The presence of plasmatic exudate in the subcutaneous connective tissue, giving rise to non-inflammatory edema, is another possible cause, together with the changes to the fundamental interstitial substance of proteoglycans.
A four stage classification of the establishment of cellulitis has been determined [Terranova F. et al., “Cellulite: nature and aetiopathogenesis”. Int. J. Cosmet. Sci., 2006, 28(3), 157-167]. Initially, phase I, the walls of the blood capillaries become more permeable and this causes blood plasma to be released from the vessels situated between the layers of adipose tissue, which leads to the appearance of edema. In the following phase II, the aggregation of adipose cells and the amplification of the fibrillar network of collagen bundles which interconnect the adipocytes prevent the circulation of blood leading to hemostasis. In phase III, the adipocytes are added forming millimeter-sized micronodules, enveloped by less mobile collagen fibers. Lastly, in phase IV many of these micronodules are added forming larger macronodules (from 2 to 20 mm), which can compress the adjoining nerve endings, causing an increase in the sensitivity of the skin of the cellulitis patient, which can become painful. It is for this reason that phase IV is considered to be pathological due to the clinical symptoms which appear, whilst the other three phases are considered to be aesthetic skin problems. It is believed that the initial phases are more or less reversible whilst the final phases are irreversible.
Both the cosmetic and pharmaceutical sector and the food sector have made various efforts to develop compounds able to regulate the volume of the adipose tissue. Examples of compounds intended to increase the volume of the adipose tissue are found in the prior art, whether they are from plant extracts, such as those described in documents U.S. Pat. No. 7,618,662 B2 and US 2003/0044475 A1 among others, compounds which are natural in origin [EP 2046283 A2] as well as compounds that are synthetic in origin [U.S. Pat. No. 5,348,943 A]. Likewise, several treatments against cellulitis whose objective is to reduce the volume of adipose tissue are available on the market. These are based principally on deep lymphatic drainage massage (manual or electromechanical), sequential pneumatic compression, electrolipolysis or mesotherapy. Physiotherapy treatments such as massages and lymphatic drainage stimulate blood and lymphatic microcirculation and increase the removal of excess fluids in the adipose tissue. Massage also has the effect of delaying the subsequent development of fibrosclerosis and the aggregation of adipocytes into nodules. These treatments are usually combined with the application of cosmetic products with anti-cellulite effectiveness. The most widely used compounds are caffeine and its derivatives, carnitine, forskolin as well as plant extracts such as those described in documents EP 2210610 A1, DE 202009010648 U1 and U.S. Pat. No. 7,410,658 B2 among others, or compounds which are natural in origin (isoflavones such as those described in document EP 1234572 A1 or menthol derivatives such as those described in international application WO 2010/089421 A2 among others).
However, despite the arsenal of existing compounds and/or extracts, the cosmetic, pharmaceutical and food industry is still interested in developing alternatives to the existing compounds capable of modulating PGC-1α.